Now how about the shape? I am a little wider on the hips than the waist and bust area. Will a straight rectangular shape down to mid hip be ok? Or would it be better if I shape it a bit wider at the bottom? If I do stockinette it curls up at the bottom and if I do entrelac I thought of leaving two little slits at the bottom sides.

I would imagine it depends on how long you want your vest. If it will be made to partially cover your hips, then you might need to add some shaping to the bottom. However, if it's somewhat shorter, then you can probably get away without sizing that part of the garment. I would measure around your waist/hips where you expect the vest to end. Then compare that measurement to the size of the garment (or a similarly fitting garment--doesn't have to be this one) a few inches below the bust. If these two measurements are similar, you probably don't need sizing for your hips. If they're different, you probably do need some increases.

Of course, you can add a border to stockinette stitch to keep it from curling, and if you go the stockinette route, you may need to add some kind of border around the underarms and neck, too. Those will curl in straight stockinette stitch, so beware!

If you use entrelac, I don't see any reason why you can't include slits--anywhere and as many as you like! They could certainly help with the fitting issue.

Do you have a similar vest that fits you well? Or any other type of sweater or shirt? I'm thinking you might use such a garment for a guide.

I think the slits at the sides are a good solution. It gives you some extra ease at the hips and if the vest is open down the front, it's still a nice look at the sides. If you're seaming the sides you can experement with how deep to make the slits.

You seem to be fairly proficient in measuring, gauging, and coming up with your own patterns. Perhaps your mom can help you with the measurements. Here's a simple baby sweater from the Lion brand site. I know you're doing an adult size, but this will give you an idea. I've converted this to knitting a baby sweater for my granddaughter and it turned out well. I like the simple rectangular shapes and the ease of construction in this. You would just need to measure the hips and length you want and divide this by two for front and back. be sure to give yourself a little extra for ease of movement, comfort, and the fact that you will be wearing a blouse under it. You have to make allowances in the pattern for that. You can do this! Welcome to the world of designing.

Thanks a lot girls. I've actually designed a vest before but it was for my daughter and only needed about 30 or so stitches each side. I followed a pattern and didn't like it so I did the whole thing again my way and loved it. Fitted really nice on her.

The thing that's putting me off a bit is the number of stitches that I'll need each side: 85/80! It will take me about a year to finish it.

Some woman told me I should do it all one piece leaving an opening for the neck. If I do decide to go ahead with it and it comes out wrong I might give it to someone rather than undoing it.